The present invention relates to devices for administering, injecting, delivering, infusing or dispensing a substance, and to methods of making and using such devices. More particularly, it relates to such a device for delivering a fluid product, wherein the device can be developed as an injection device for the injection of an adjustable dose of the product and can take the form of an injection pen, i.e. a compact injection device in pen-like form.
A large number of injection devices are known from the prior art for the dosed administering of medicaments or therapeutic agents such as insulin, growth hormones or osteoporosis drugs, which must be administered regularly. Such devices are on the one hand intended to reliably and precisely deliver a dose which is able to be pre-set. On the other hand, they are intended to be user-friendly to a high degree. This applies all the more because they are generally operated by a person for self-administration.
The medicament can be housed in an exchangeable carpule (which also may be thought of and/or referred to as an ampoule, receptacle, container or reservoir), which is able to be inserted into a carpule holder. The latter can then be associated with or fastened to a housing of the injection device, e.g. by a screw connection or a bayonet connection. For distribution, a product stopper or piston in the carpule is pushed forward (toward the needle associated with the injection device) by a delivery arrangement with a delivery element in the form of a piston rod.
Compact, pen-shaped administering devices are known, in which the distribution takes place automatically after a first triggering (e.g. “power-assisted pens”). The dose in such devices is generally pre-set by a rotation of a dosing button. A drive is present in the device, e.g. a spring drive, which is tensioned on setting of the dose. The device is triggered by pressing a triggering arrangement, which can be identical to the dosing button. In so doing, the drive generates a drive movement, e.g. in the form of a rotary movement, which is converted into an advancing movement of the piston rod. In the case of a drive by a rotary movement, the piston rod may be constructed as a threaded rod on which a drive nut runs. Examples of such injection pens are disclosed in DE-A 10 2004 063 644, DE-A 10 2004 063 647, WO-A 2004/002556 and DE-A 102 29 122.
In EP-A 1 681 070, a manually driven injection pen is disclosed, wherein the piston rod is hollow and has an internal thread instead of an external thread. This internal thread is in engagement with the external thread of a rotatable drive shaft, which, in the region of its proximal end, is mounted opposite an inner housing part. The piston rod has on its outer side continuous longitudinal grooves into which projections of a fixing bush engage. This fixing bush is secured relative to the housing when a receptacle holder is connected with the housing, and can freely rotate when the receptacle holder is detached from the housing. On administering of a dose, the drive shaft rotates and thereby advances the piston rod linearly, which is guided to be locked against relative rotation via the fixing bush. In the case of a change of reservoir, the receptacle holder is detached from the housing. Thereby, the fixing bush, and with it also the piston rod, is freely rotatable with respect to the housing. When the piston rod is pushed into the housing, the drive shaft remains stationary and the piston rod performs a screw motion.
This device is capable of improvement in several respects. For example, the screw motion of the piston rod compulsorily requires, on insertion, that at its distal end a cap is rotatably mounted, which, on insertion, does not co-rotate with the piston rod, because otherwise on insertion no suitable counter-surface would be available which is locked against relative rotation, on which the axial force, required for insertion, could engage. Furthermore, the presence of the fixing bush requires that longitudinal grooves are formed on the outer side of the piston rod. Dirt can accumulate in these. Moreover, a bearing of the drive shaft relative to the housing in its proximal end region is disadvantageous, because a large amount of space is required for this in a region in which otherwise, for example, drive components could be housed. Also, in this device it is not ensured that the piston rod also actually touches the stopper of the medicament reservoir.